The objectives are to investigate the relationship between motor activity and heart rate responses, to evaluate the sensitivity of these responses to associative and non-associative variables and to determine the extent to which these responses are mediated by common processes. These objectives will be approached through four interrelated project areas: l. Since activity in an aversive learning situation is a U- shaped function of time since initial training, the contributions of associative and nonassociative factors to changes in activity and heart rate responses will be studied as a function of initial training-retest interval. 2. Unconditioned heart rate and activity responses to various stimuli will be assessed before these stimuli are used in discriminated Y-maze avoidance. An analysis in terms of orienting and defensive responses will contribute to an understanding of stimulus effects in avoidance learning. 3. The relationships among heart rate, general motor activity and response suppression will be studied in a situation which provides slow acquisition and subsequent temporal discrimination of response suppression. 4. Strain differences in avoidance performance have been attributed to nonassociative, activity- related variables. These strains also differ in heart rate baseline and responsiveness to shock. Pure strain and cross bred offspring will differ under the conditions of projects I, II, and III which will provide data relevant to the main objectives as well as to an understanding of genetic determinants of behavior.